This invention relates to an apparatus and method for anchoring sutures to a live human bone. More particularly, this invention relates to a suture anchor made of a substantially rigid, preferably biocompatible material, and most preferably a material that can be incorporated into the bone as a bone graft, such as bone, and an insertion tool having a portion made of a stress-induced shape memory material which is inserted into the anchor and functions to orient the suture anchor, once inserted in the bone, to securely anchor the suture.
Suture anchors for anchoring a suture to bone so that another body tissue, such as muscle or ligament, may be sutured to the bone are known in the art. Such suture anchors come in a variety of shapes and designs. A survey of such suture anchors may be found in James E. Carpenter et al., "Pull-Out Strength of Five Suture Anchors", Arthroscopy, 9(1), pp. 109-113 (1993).
For example, harpoon-type or screw-type suture anchors are drilled into cortical bone. Examples of such suture anchors are shown, for example, in Cerrier et al. U.S. Pat. No. 5,100,417 and Hayhurst et al. Canada Patent No. 2,045,903. Such suture anchors are held in place in any of a variety of manners, such as through self-tapping, by a force fit, or by including a resilient portion which flexes to frictionally engage the bone material.
Another type of suture anchor includes a rigid member and a resilient, shape memory member. The resilient member is substantially flush with the rigid member during insertion, and flexes away from the rigid member once lodged inside the bone. Such anchors have been described in Gatturna et al. U.S. Pat. Nos. 5,046,513 and 5,192,303. The shape memory material may be made in accordance with, for example, Quin U.S. Pat. No. 4,505,767 or Harrison U.S. Pat. No. 4,565,589. Because two different materials are used, this type of suture anchor can be costly and difficult to manufacture. Moreover, the joining of two dissimilar metals leads to potential flaws and potential breakage at the joint or weld point.
A third type of suture anchor is substantially elongated and is inserted with its longitudinal axis substantially parallel to the bone hole through which it is inserted. The suture anchor is then reoriented upon reaching cancellous bone tissue by pulling on the suture attached at a selected point along the suture anchor. Examples of such suture anchors are shown in Hayhurst et al. U.S. Pat. No. 5,041,129 ("Hayhurst") and Noblitt et al. U.S. Pat. No. 5,203,787 ("Noblitt"). The Hayhurst suture anchor has a substantially cylindrical rigid body with a central bore and a longitudinal slot extending from one end to approximately the middle of the rigid body. A suture is positioned inside the central bore, and the anchor is inserted with the slot entering the bone last. Once the anchor is properly positioned, the suture is pulled through the slot towards the base of the slot, thereby reorienting the suture anchor to fix the anchor in the bone. The Noblitt suture anchor has an offset portion at which a suture is attached. Once the suture anchor is within cancellous tissue, the suture is pulled, thereby reorienting the suture anchor so that its longitudinal axis is substantially transverse to the bone hole through which it was inserted. One disadvantage associated with this type of anchor is that tugging on the suture to reorient the anchor may put undue stress on the suture (particularly at the base of the slot in Hayhurst). Moreover, the introduction technique is unduly complicated, requiring several types of insertion tools (Noblitt may provide additional complications because of the nonuniform thickness of the suture anchor along the longitudinal axis). Furthermore, Hayhurst's slot may structurally weaken the remainder of the suture anchor body, and Noblitt's elongated, narrow ends may tend to break off during reorientation.
A disadvantage common to all of the above-described suture anchors is that many are typically formed of metal which may not be biocompatible. Additionally such suture anchors are typically visible during X-ray, magnetic resonance imaging (MRI), and computerized tomography (CT) examinations. Accordingly, these suture anchors may interfere with noninvasive examinations of the treated area. Moreover, the above-described suture anchors typically require complex insertion tools, the use of which is time consuming. There is thus greater potential for later complications such as bone weakening.
Two other anchoring means are staples and cement. The former is generally not desirable because staples can crack the bone in which they are inserted or damage the tissue to be connected to the bone. The latter is generally not desirable because of substance compatibility, the need for particular surface characteristics for adequate bonding, and excessive setting times.
It therefore would be desirable to provide an apparatus for anchoring a suture to a bone which is simple to manufacture and to insert, which does not interfere with noninvasive examinations such as radiographs, MRI, or CT, and which is biocompatible and most preferably, capable of being incorporated into the bone as a bone graft, to strengthen the bone. Alternatively, the apparatus may be bioabsorbable.
It would also be desirable to provide a method and apparatus for inserting a suture anchor which results in a minimal number of insertion steps and requires a minimal number of tools.